a gis landslide database of northern portugal supported by

7th EUREGEO 2012
Session 1 - Oral presentation
A GIS LANDSLIDE DATABASE OF NORTHERN PORTUGAL SUPPORTED BY
DOCUMENTAL SOURCES
Susana Pereira(1); José Luís Zêzere (1) and Ivânia Daniela Quaresma (1)
(1) Riskam, Centre of Geographical Studies, University of Lisbon. Edifício da Faculdade de Letras da
Universidade de Lisboa. Alameda da Universidade | 1600-214 Lisboa | Portugal. susana-pereira@
campus.ul.pt
documental sources?
KEY WORDS: Landslides; Northern Portugal;
Disaster Databases.
METHODOLOGY
INTRODUCTION
The NPLD is a geodatabase that includes the
following information for each landslide occurrence:
ID, date and hour of occurrence, location, x and
y coordinates, landslide type, data source, and
damages (fatalities, injuries, homeless people,
disruptions in rail and road circulation and destructed
buildings).
Data collection was exclusively based on
documental sources: regional newspapers (daily
and weekly), academic works and reports of
the civil protection authorities. Most of landslide
occurrences (68.6%) were identified in newspapers
while landslides reported by the civil protection and
academic works are only 26.1% and 5.3% of total,
respectively.
Documental sources were carefully analyzed in
order to identify and georeference landslides. Road
maps, rail road maps and the Google Earth were
used as additional tools to support the location of
slope movements. Landslides were mapped in
topographic maps (1:25 000 scale) with a point in
the centroid of the rupture zone.
When descriptions about landslide location were
not enough precise landslides were mapped in the
parish centroid.
Spatial and temporal distribution of landslides
belonging to NPLD was compared with a national
database (Quaresma, 2008) of landslide damaging
events occurred in Portugal, which generated
fatalities, injuries, missing people, homeless and
evacuated people. This database was originally for
the period 1900-2008 and was further updated until
2010.
In recent years a huge effort to collect, record
and analyze information about disasters occurrence
and impacts has been made worldwide.
The development of natural disasters databases
is crucial for risk management purposes, because it
allows improving systems of indicators on disaster
risk and vulnerability at national and sub-national
scales. In addition, the analysis of social, economic
and environmental impact of disasters needs to be
transferred to decision-makers and integrated in
land use management and civil protection policies
in order to prevent and mitigate disaster losses.
Landslides databases are essential to assess
landslide hazard and risk. However, landslide
databases may have different spatial resolution
associated with different goals, scale and data
capture methods. Limitations related with spatial
resolution and data capture procedures of landslide
databases need to be considered when data is
transferred and applied by end-users.
STUDY AREA AND OBJECTIVES
During the last century, Portugal was affected
by several destructing natural disasters, namely of
hydrologic (floods) and geomorphologic (landslides)
origin. The basic information on past damaging
landslides occurred in Portugal from 1900 to 2008
can be found in the academic work performed at
national scale by Quaresma (2008).
At the regional scale, a landslide database was
made for the North Region of Portugal including
the complete landslides occurrences identified
exploring documental sources for the period lasting
from 1900 to 2008 (Pereira, 2010).
In this work we present the Northern Portugal
Landslide Database (NPLD) which was updated to
2011. In particular we want to answer the following
questions: (1) What is the degree of completeness
and the temporal and spatial accuracy of landslide
distribution? (2) What are the advantages and
limitations of landslides databases supported by
RESULTS
The NPLD has 640 occurrences, 79% of them
georeferenced in the centroid of the landslide
rupture zone (Fig. 1, Table 1). The National
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7th EUREGEO 2012
database has only 63 landslides, which is explained
by the criteria used for landslide inventory (Table 1).
Nevertheless, the spatial distribution of landslides
of both databases is quite similar. Landslides are
located mainly along the Douro valley and in the
Oporto metropolitan area.
Falls and debris flows are the most frequent
landslides within the NPLD. More than half of these
Session 1 - Oral presentation
landslides caused disruptions in railroad and road
circulation (37.5% correspond to line closed and
13.3% to road block).
More than 70% of landslides of the NPLD occurred
in winter rainy months, especially in December
(31%) and January (24.5%). The National database
has the same monthly landslide distribution.
Figure 1 – Landslides distribution in the Northern Portugal according to the national and regional landslide databases.
For a similar reference period, the NPLD includes
a higher number of deaths and homeless people in
comparison with the national database. Therefore,
we can conclude that information reported by
newspapers at the national level (used to construct
the national database) is not enough representative
of landslide damages occurred at the regional scale.
In addition, the regional newspapers also provide
more accurate information regarding location of
landslides.
Period
Main Sources
Nr. landslides
Landslides/year
Nr georeferenced
landslides
Georeferencing
Criteria for landslide
inventory
Northern Portugal Landslide
Database
National Database
1900-2011
1900-2010
Regional newspapers (daily and
weekly)
640
5.8
National newspaper (daily)
505
Point (centroid of landslide)
63
Point (nearest toponymy)
All landslides
Landslides that caused
fatalities, injuries, missing
people, homeless and
evacuated people
CONCLUSIONS
Temporal distribution of landslides is strongly
associated with wet months reflecting the rainfall
triggering of slope movements. Although the NPLD
theoretically includes all landslides, in practice
the spatial distribution of landslides reflects
the pattern of landslides that generated direct
damages in population (e.g. fatalities, injuries,
homeless), buildings and infra-structures (e.g. road,
railroads). Therefore, landslide inventories based
in documental sources can be easily transferred to
emergency planning and societal risk assessment.
Nevertheless, these landslide inventories are not
enough complete to generate landslide susceptibility
assessment which is crucial for land use planning.
63
0.6
Nr. deaths
129
60
Nr. injuries
124
122
Nr. homeless
381
279
REFERENCES
PEREIRA S. (2010) -. Perigosidade a Movimentos de
Vertente na Região Norte de Portugal. Dissertação de
doutoramento, Faculdade de Letras da Universidade
do Porto, 2010.
QUARESMA I. (2008) – Inventariação e análise de eventos hidro-geomorfológicos com carácter danoso em
Portugal Continental. Dissertação de Mestrado, Faculdade de Letras da Universidade de Lisboa.
Table 1 – Landslide databases details.
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